US20200007189A1 - Crosstalk reduction in receiver inductive loop using capturing loop in transmitting inductive loop - Google Patents
Crosstalk reduction in receiver inductive loop using capturing loop in transmitting inductive loop Download PDFInfo
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- US20200007189A1 US20200007189A1 US16/021,175 US201816021175A US2020007189A1 US 20200007189 A1 US20200007189 A1 US 20200007189A1 US 201816021175 A US201816021175 A US 201816021175A US 2020007189 A1 US2020007189 A1 US 2020007189A1
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- 230000001939 inductive effect Effects 0.000 title claims abstract description 194
- 230000004907 flux Effects 0.000 claims abstract description 19
- 239000003990 capacitor Substances 0.000 claims description 12
- 239000004020 conductor Substances 0.000 claims description 7
- 238000013461 design Methods 0.000 description 17
- 238000002955 isolation Methods 0.000 description 13
- 230000008878 coupling Effects 0.000 description 8
- 238000010168 coupling process Methods 0.000 description 8
- 238000005859 coupling reaction Methods 0.000 description 8
- 238000010586 diagram Methods 0.000 description 8
- 238000012546 transfer Methods 0.000 description 6
- 230000004888 barrier function Effects 0.000 description 5
- 238000013459 approach Methods 0.000 description 3
- 238000004519 manufacturing process Methods 0.000 description 2
- 238000000034 method Methods 0.000 description 2
- 230000009471 action Effects 0.000 description 1
- 230000005540 biological transmission Effects 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 238000006880 cross-coupling reaction Methods 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 230000005669 field effect Effects 0.000 description 1
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- 239000004065 semiconductor Substances 0.000 description 1
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B3/00—Line transmission systems
- H04B3/02—Details
- H04B3/32—Reducing cross-talk, e.g. by compensating
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
- H04B1/06—Receivers
- H04B1/10—Means associated with receiver for limiting or suppressing noise or interference
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L25/00—Baseband systems
- H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
- H04L25/026—Arrangements for coupling transmitters, receivers or transceivers to transmission lines; Line drivers
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L25/00—Baseband systems
- H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
- H04L25/0264—Arrangements for coupling to transmission lines
- H04L25/0272—Arrangements for coupling to multiple lines, e.g. for differential transmission
Definitions
- the field is digital isolators.
- Digital isolators are used to allow signal transfer between environments that must remain electrically isolated.
- the simplest form of a digital isolator is an opto-coupler.
- a signal is provided to drive a photodiode.
- a phototransistor is configured to receive the light emitted from the photodiode.
- Electrical isolation is provided between the photodiode and the phototransistor simply by an air gap through which the light passes.
- opto-couplers do not provide adequate performance. Therefore, another class of digital isolators has developed which utilize a capacitive isolation barrier.
- Capacitive isolation digital isolators have lower current requirement and higher frequency response, in general, than opto-couplers. However, modern ultralow power requirements have made even the lower power levels of capacitive isolation digital isolators insufficient in many instances.
- Inductive loop digital isolators have been developed where a magnetic field is used to transfer energy across an isolation barrier, rather than the capacitive transfer of capacitive isolation digital isolators.
- digital isolators include a plurality of different channels in a single chip to provide higher densities. In some cases those multi-channel digital isolators have paths going in different directions. While this is not an issue for capacitive isolation digital isolators, this bi-directional configuration results in the potential for undesired crosstalk or cross-coupling in an inductive loop or transformer digital isolator.
- Various approaches can be used to minimize the crosstalk but those approaches either utilize much more space, by increasing inter-channel spacing, or reduce circuit values. Another approach stacks the receive and transmit inductive loops vertically, but this makes manufacturing much more challenging.
- the transmitter and receiver inductive loops of a given channel are coplanar.
- the receiver inductive loops of a given channel include a large, generally conventional loop portion and a small loop portion that is located inside the transmitter inductive loops of the adjacent channels.
- the sizes of the small loop portion and the conventional loop portion are generally in the ratio of the magnetic flux in the conventional loop portion to the magnetic flux in the transmitter inductive loop. This size relationship results in the voltage of the small loop portion being very close but opposite in sign to the voltage in the conventional loop portion.
- FIG. 1 is a block diagram of a sensor including a multi-channel, inductive coupling digital isolator.
- FIGS. 1A-1 to 1A-4 are block diagrams providing more details on the digital isolator of FIG. 1 .
- FIG. 2 is a diagram illustrating configuration of and crosstalk between two channels of a multi-channel, inductive coupling digital isolator.
- FIG. 3 is a side view diagram illustrating crosstalk between two channels of a multi-channel, inductive coupling digital isolator.
- FIG. 4 is a diagram illustrating configuration of two channels of a multi-channel, inductive coupling digital isolator using first alternate receiver loop configuration.
- FIG. 5 is a diagram illustrating configuration of two channels of a multi-channel, inductive coupling digital isolator using shielding around the loops.
- FIG. 6 is a graph illustrating impedance of the transmitter inductive loops of FIGS. 2, 4 and 5 .
- FIG. 7 is a graph illustrating crosstalk of the receiver inductive loops of FIGS. 2, 4 and 5 .
- FIG. 8 is a diagram illustrating configuration of two channels of a multi-channel, inductive coupling digital isolator having reduced crosstalk.
- FIG. 9 is a diagram illustrating the two channels of a multi-channel, inductive coupling digital isolator having reduced crosstalk in the configuration of FIG. 2 .
- FIG. 10 is a graph illustrating impedance of the transmitter inductive loops of FIGS. 2 and 6 .
- FIG. 11 is a graph illustrating crosstalk of the receiver inductive loops of FIGS. 2 and 6 .
- a sensor module 100 includes a sensor circuit 102 which is connected to various sensors 104 that are being monitored.
- a microcontroller 106 provides the intelligence for the sensor module 100 .
- An input/output (I/O) circuit 108 is connected to the microcontroller 106 and to a main controller no to provide the sensor readings to the main control system.
- the sensor circuit 102 and the microcontroller 106 are connected by a digital isolator 112 .
- the digital isolator 112 is a four channel device with three channels being connected to transfer data from the microcontroller 106 to the sensor circuit 102 and one channel connected to transfer data from the sensor circuit 102 to the microcontroller 106 .
- the digital isolator 112 is an inductive isolation device which uses inductive loops to transfer the signal across the isolation barrier.
- Receiver circuitry 114 A receives the output signal from the OUT 1 output of the microcontroller 106 .
- Receiver circuitry 114 B receives the output signal from the microcontroller 106 OUT 2 output, while receiver circuitry 114 C receives the OUT 3 signal from the microcontroller 106 .
- the outputs of the receiver circuitry 114 A, 114 B, 114 C are provided to transmitter inductive loops 116 A, 116 B, 116 C.
- Receiver inductive loops 118 A, 118 B, 118 C are coupled to the transmitter inductive loops 116 A, 116 B, 116 C.
- Drivers 120 A, 120 B and 120 C are connected to the receiver inductive loops 118 A, 118 B, 118 C.
- the driver 120 A is connected to the DIN or data input pin of the sensor circuit 102 .
- the driver 120 B is connected to the SCLK or serial clock input of the sensor circuit 102 .
- the driver 120 C is connected to the CS or chip select input of the sensor circuit 102 .
- the DOUT or data out or ready signal from the sensor circuit 102 is provided to receiver circuitry 122 .
- the receiver circuitry 122 is connected to the transmitter inductive loop 124 , which is coupled to the receiver inductive loop 126 .
- a driver 128 is connected to the receiver inductive loop 126 and is connected to the IN 1 signal of the microcontroller 106 .
- the digital isolator 112 handles the signals for a serial interface between the microcontroller 106 and the sensor circuit 102 . It is understood that this is just a simple example to illustrate the use of digital isolators, particularly multichannel isolators where data flows in different directions in the particular isolator.
- FIGS. 1A-1 to 1A-4 provide more details of the circuitry inside the inductive isolation digital isolator 112 . As the four channels are identical electrically, so only a single channel is described here.
- the input signal to the receiver circuitry 122 controls a switch 150 .
- the switch 150 is connected between a current source 152 connected to ground and a bridge circuit 154 .
- the bridge circuit 154 is formed by cross-coupled n-channel and p-channel enhancement metal-oxide-semiconductor field-effect transistor (MOSFET) pairs 156 and 158 .
- MOSFET metal-oxide-semiconductor field-effect transistor
- the first pair 156 has the source of a p-channel enhancement MOSFET 160 connected to VDD and the gates of the p-channel enhancement MOSFET 160 and an re-channel enhancement MOSFET 162 connected.
- the source of the n-channel enhancement MOSFET 162 is connected to the switch 150 .
- the second pair has the source of a p-channel enhancement MOSFET 164 connected to V DD and the gates of the p-channel enhancement MOSFET 164 and an n-channel enhancement MOSFET 166 connected.
- the source of the n-channel enhancement MOSFET 166 is connected to the switch 150 .
- the drains of the p-channel enhancement MOSFET 160 and the n-channel enhancement MOSFET 166 are connected and provide a TXP or transmit positive signal.
- the drains of the p-channel enhancement MOSFET 164 and the n-channel enhancement MOSFET 162 are connected and provide a TXM or transmit minus signal.
- the TXP and TXM signals are provided to the transmitter inductive loop 124 and a parallel capacitor 168 .
- the parallel capacitor 168 can be a separate capacitor or can be the inherent capacitance of the transmitter inductive loop 124 .
- a channel 170 is the isolation between the transmitter inductive loop 124 and the receiver inductive loop 126 . In this configuration the MOSFETs 160 , 162 , 164 and 166 act as an oscillator at the resonant frequency of the transmitter inductive loop 124 and the capacitor 168 .
- the RXP or receive positive and RXM or receive minus signals are developed across the receiver inductive loop 126 and a parallel capacitor 172 .
- the parallel capacitor 172 can be a separate capacitor or can be the inherent capacitance of the transmitter inductive loop 126 .
- the RXP signal is provided to the gate of an n-channel enhancement MOSFET 174
- the RXM signal is provided to the gate of an n-channel enhancement MOSFET 176 .
- the drains of the n-channel enhancement MOSFET 174 and the n-channel enhancement MOSFET 176 are connected to V DD .
- the sources of the n-channel enhancement MOSFET 174 and the n-channel enhancement MOSFET 176 are connected to a current source 178 , which is connected to ground.
- a capacitor 180 is provided in parallel with the current source 178 .
- the MOSFETs 174 and 176 act as a rectifier.
- the connection of the sources of the n-channel enhancement MOSFET 174 and the n-channel enhancement MOSFET 176 is also provided to the non-inverting input of a comparator 182 , with the inverting input connected to V REF .
- the output of the comparator 182 is the output of the digital isolator 112 .
- the switch 150 In operation, when the input is a one or high, the switch 150 is closed and the bridge circuit 154 is driving the transmitter inductive loop 124 to create the magnetic field captured by the receiver inductive loop 126 .
- the signal from the receiver inductive loop 126 is rectified and compared to a reference. As the switch 150 is closed, the rectified voltage will exceed the reference and the comparator 182 will drive a high or one output.
- the switch 150 When the input signal is low, the switch 150 is open and there is no magnetic field produced by the transmitting inductive loop 124 , so the rectified voltage will be low, below the reference, and the output of the comparator 182 is low or zero.
- FIG. 2 illustrates an arrangement of loops and inductive loops according to the prior art.
- a first channel 202 has data flowing in one direction, while a second channel 204 has data flowing in an opposite direction.
- the data in the first channel 202 is provided to a TX 1 transmitter inductive loop 206 , which is coupled to an RX 1 receiver inductive loop 208 .
- a TX 2 transmitter inductive loop 210 receives the data being transmitted on channel 2 and couples to an RX 2 receiver inductive loop 212 to provide the data.
- the four inductive loops 206 , 208 , 210 , 212 are arranged in a grid.
- the transmitter and receiver inductive loops 206 , 208 and 210 , 212 of a given channel 202 , 204 are located 700-1000 ⁇ m apart in one design and are substantially coplanar as they are formed in the same process steps in one design.
- the transmitter and receiver inductive loops 206 , 208 , 210 , 212 are formed from seven to eight turns of the conductor. Being substantially coplanar allows the digital isolator to formed using conventional integrated circuit processing techniques and does not require elaborate three dimensional structures.
- Each inductive loop 206 , 208 , 210 , 212 has a size of approximately 400 ⁇ m by 200 ⁇ m in one design.
- the transmitter inductive loops 206 , 210 of one channel are located 300-500 ⁇ m from the receiver inductive loop 212 , 208 of the other channel. Dimensions are provided on FIG. 2 , which is not drawn to scale for illustrative purposes. These dimensions and numbers of turns are design-based and can vary as needed for a particular design.
- FIG. 2 shows exemplary magnetic flux lines 220 emanating from TX 2 transmitter inductive loop 210 .
- the magnetic flux density in the RX 2 receiver inductive loop 212 is not dissimilar to the magnetic flux density in the RX 1 receiver inductive loop 208 . This leads to a situation where the TX 2 to RX 1 crosstalk may actually exceed the TX 1 to RX 1 signal itself.
- the desired signal level is 320 mV while the crosstalk is 515 mV, actually higher than the signal level. This would result in significant data transmission errors.
- FIG. 3 is an alternate view of the inductive loops of FIG. 2 .
- the view of FIG. 3 is a side view, which shows that the third dimension of the magnetic flux lines 220 and the substantially coplanar nature of the adjacent channels.
- FIG. 4 shows a transmitter inductive loop 402 similar to the transmitter inductive loops 206 and 210 but a second design of a receiver inductive loop 404 .
- the receiver inductive loop 404 has been reconfigured to be in roughly a FIG. 8 shape. Referring to FIG. 7 , this configuration of the receiver inductive loop 404 does reduce the crosstalk to a value of 30 mV but at the disadvantage of changing the impedance of the inductive loops.
- An inductive loop such as those of receiver inductive loop 208 and receiver inductive loop 212 have a tank impedance of 1.1 k ⁇ , while the configuration of FIG. 4 has a tank impedance of 450 ⁇ . This reduced impedance results in a reduced Q for the loop. Reducing the Q of the loop has the undesirable effect of impacting the signal-noise ratio (SNR) of the circuits, which complicates the entire design.
- SNR signal-noise ratio
- FIG. 5 A alternative design is illustrated in FIG. 5 , where the inductive loops of FIG. 2 , referred to in FIG. 5 as a transmitter inductive loop 502 and a receiver inductive loop 504 , are encircled by shielding 506 and 508 .
- the shielding does reduce the crosstalk as indicated in FIG. 7 , where the crosstalk is reduced to the 160 mV but the presence of the shielding also further decreases the tank impedance to 620 ⁇ as shown in FIG. 6 , again causing the impedance problems.
- the Q of the loop can be maintained but only at the expense further separating the various loops as greater distance is needed between the shields and the loops, which increase chip size undesirably.
- FIG. 8 is a drawing of a reduced crosstalk configuration which still maintains high impedance and high Q for the loops.
- the transmitter inductive loop 802 is configured similarly to that of the FIG. 2 prior art, such as transmitter inductive loops 206 and 210 .
- a receiver inductive loop 804 is divided into two portions.
- a first portion 806 is a conventional portion, while a second portion 808 is added which interacts with the flux lines inside the transmitter inductive loop 802 . This means that the receiver inductive loop 804 is coupling with both positive and negative flux lines and their values are being summed.
- any crosstalk based on a signal from the transmitter inductive loop 802 is greatly reduced.
- the crosstalk on the RX receiver inductive loop 804 based on the TX transmitter inductive loop 802 is given by the following equation, where X is the RX receiver inductive loop 804 and Y is the TX transmitter inductive loop 802 :
- V X B Y dA X
- B is the magnetic flux density
- d is the distance
- A is the area
- the equation is modified to account for the separate areas and the inversion of the magnetic flux between the two portions 806 , 808 .
- V X B +Y dA X1 + B ⁇ Y dA X2
- the ratio of B +Y :B ⁇ Y was 95:5, as the magnetic flux inside the loop is much greater than the magnetic flux outside the loop.
- the area of X2, first portion 806 needs to be 95 times the size of the area of X1, second portion 808 .
- This ratio will vary based on many factors, including loop size, loop spacing, number of turns and the like.
- a ratio this size also means that the Q of the receiver inductive loop 804 is very close to the Q of the receiver inductive loop 208 , so that the impedance and other loop properties are effectively unchanged from the original receiver inductive loop 208 .
- FIG. 11 illustrates the crosstalk change between the receiver inductive loop 208 and the receiver inductive loop 804 .
- the 515 mV level of the noise without crosstalk cancellation according to FIG. 2 is illustrated in comparison to the 320 mV normal signal for the channel and the greatly reduced 20 mV signal for the crosstalk for the design of FIG. 8 , where the receiver inductive loop has the two portions.
- FIG. 10 illustrates that the impedance of the receiver inductive loop of FIG. 8 with the two portions is only nominally less than the receiver inductive loop of the prior art design of FIG. 2 , which allows simplified circuit design.
- FIG. 9 illustrates the design of FIG. 8 for two channels in different directions.
- a first channel TX 1 transmitter inductive loop 902 is associated with a first channel RX 1 receiver inductive loop 904 .
- a second channel TX 2 transmitter inductive loop 906 is associated with a second channel RX 2 receiver inductive loop 908 .
- the distances between the various transmitter inductive loops 902 , 906 and the various receiver inductive loops 904 , 908 represent the isolation barriers between them.
- the transmitter inductive loop and the receiver inductive loop of a given channel are on separate dies, though the transmitter inductive loop and the receiver inductive loop would be on the same die.
- the receiver inductive loop 908 for the second channel is receiving the normal amount of flux lines but the receiver inductive loop 904 of the first channel has minimal signal crosstalk because of the action of the second portion 905 located inside the transmitter inductive loop 906 of the second channel.
- the inductive loops of the third and fourth channels are not illustrated by the receiver inductive loops do not contain the second portion located in the transmitter inductive loop of a different channel as the receiver inductive loop of the third channel is adjacent the receiver inductive loop of the second channel and not the transmitter inductive loop, as the channels are flowing data in the same direction.
- the receiver inductive loop of the third channel is adjacent the receiver inductive loop of the fourth channel and not the transmitter inductive loop, as the channels are flowing data in the same direction.
- the receiver inductive loops with the portions inside the transmitter inductive loops are only needed for adjacent channels where data is flowing in different directions.
- the crosstalk is reduced so that a more manufacturable coplanar configuration can be used but the inductive loops can still be more compactly arranged.
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Abstract
Description
- The field is digital isolators.
- Digital isolators are used to allow signal transfer between environments that must remain electrically isolated. The simplest form of a digital isolator is an opto-coupler. In an opto-coupler a signal is provided to drive a photodiode. A phototransistor is configured to receive the light emitted from the photodiode. Electrical isolation is provided between the photodiode and the phototransistor simply by an air gap through which the light passes. However, there are many circumstances where opto-couplers do not provide adequate performance. Therefore, another class of digital isolators has developed which utilize a capacitive isolation barrier. Effectively one plate of a capacitor is present on the input side and the other plate of the capacitor is present on the output side, with the capacitive isolation barrier separating the capacitor plates. Capacitive isolation digital isolators have lower current requirement and higher frequency response, in general, than opto-couplers. However, modern ultralow power requirements have made even the lower power levels of capacitive isolation digital isolators insufficient in many instances.
- Inductive loop digital isolators have been developed where a magnetic field is used to transfer energy across an isolation barrier, rather than the capacitive transfer of capacitive isolation digital isolators. Often digital isolators include a plurality of different channels in a single chip to provide higher densities. In some cases those multi-channel digital isolators have paths going in different directions. While this is not an issue for capacitive isolation digital isolators, this bi-directional configuration results in the potential for undesired crosstalk or cross-coupling in an inductive loop or transformer digital isolator. Various approaches can be used to minimize the crosstalk but those approaches either utilize much more space, by increasing inter-channel spacing, or reduce circuit values. Another approach stacks the receive and transmit inductive loops vertically, but this makes manufacturing much more challenging.
- In an inductively coupled multi-channel digital isolator the transmitter and receiver inductive loops of a given channel are coplanar. In the case where two adjacent channels flow data in opposite directions, the receiver inductive loops of a given channel include a large, generally conventional loop portion and a small loop portion that is located inside the transmitter inductive loops of the adjacent channels. The sizes of the small loop portion and the conventional loop portion are generally in the ratio of the magnetic flux in the conventional loop portion to the magnetic flux in the transmitter inductive loop. This size relationship results in the voltage of the small loop portion being very close but opposite in sign to the voltage in the conventional loop portion. As a result, there is minimal crosstalk from the transmitter inductive loop of one channel to the receiver inductive loop of the adjacent channel. This allows a more densely packed and coplanar arrangement of the inductive loops, making manufacturing more cost effective.
- For a detailed description of various examples, reference will now be made to the accompanying drawings in which:
-
FIG. 1 is a block diagram of a sensor including a multi-channel, inductive coupling digital isolator. -
FIGS. 1A-1 to 1A-4 are block diagrams providing more details on the digital isolator ofFIG. 1 . -
FIG. 2 is a diagram illustrating configuration of and crosstalk between two channels of a multi-channel, inductive coupling digital isolator. -
FIG. 3 is a side view diagram illustrating crosstalk between two channels of a multi-channel, inductive coupling digital isolator. -
FIG. 4 is a diagram illustrating configuration of two channels of a multi-channel, inductive coupling digital isolator using first alternate receiver loop configuration. -
FIG. 5 is a diagram illustrating configuration of two channels of a multi-channel, inductive coupling digital isolator using shielding around the loops. -
FIG. 6 is a graph illustrating impedance of the transmitter inductive loops ofFIGS. 2, 4 and 5 . -
FIG. 7 is a graph illustrating crosstalk of the receiver inductive loops ofFIGS. 2, 4 and 5 . -
FIG. 8 is a diagram illustrating configuration of two channels of a multi-channel, inductive coupling digital isolator having reduced crosstalk. -
FIG. 9 is a diagram illustrating the two channels of a multi-channel, inductive coupling digital isolator having reduced crosstalk in the configuration ofFIG. 2 . -
FIG. 10 is a graph illustrating impedance of the transmitter inductive loops ofFIGS. 2 and 6 . -
FIG. 11 is a graph illustrating crosstalk of the receiver inductive loops ofFIGS. 2 and 6 . - Referring now to
FIG. 1 , an example use of a digital isolator is provided. Asensor module 100 includes asensor circuit 102 which is connected tovarious sensors 104 that are being monitored. Amicrocontroller 106 provides the intelligence for thesensor module 100. An input/output (I/O)circuit 108 is connected to themicrocontroller 106 and to a main controller no to provide the sensor readings to the main control system. Thesensor circuit 102 and themicrocontroller 106 are connected by adigital isolator 112. Thedigital isolator 112 is a four channel device with three channels being connected to transfer data from themicrocontroller 106 to thesensor circuit 102 and one channel connected to transfer data from thesensor circuit 102 to themicrocontroller 106. Thedigital isolator 112 is an inductive isolation device which uses inductive loops to transfer the signal across the isolation barrier.Receiver circuitry 114A receives the output signal from the OUT1 output of themicrocontroller 106.Receiver circuitry 114B receives the output signal from themicrocontroller 106 OUT2 output, whilereceiver circuitry 114C receives the OUT3 signal from themicrocontroller 106. The outputs of thereceiver circuitry inductive loops inductive loops inductive loops Drivers inductive loops driver 120A is connected to the DIN or data input pin of thesensor circuit 102. Thedriver 120B is connected to the SCLK or serial clock input of thesensor circuit 102. Thedriver 120C is connected to the CS or chip select input of thesensor circuit 102. The DOUT or data out or ready signal from thesensor circuit 102 is provided toreceiver circuitry 122. Thereceiver circuitry 122 is connected to the transmitterinductive loop 124, which is coupled to the receiverinductive loop 126. Adriver 128 is connected to the receiverinductive loop 126 and is connected to the IN1 signal of themicrocontroller 106. Thus, thedigital isolator 112 handles the signals for a serial interface between themicrocontroller 106 and thesensor circuit 102. It is understood that this is just a simple example to illustrate the use of digital isolators, particularly multichannel isolators where data flows in different directions in the particular isolator. -
FIGS. 1A-1 to 1A-4 provide more details of the circuitry inside the inductive isolationdigital isolator 112. As the four channels are identical electrically, so only a single channel is described here. The input signal to thereceiver circuitry 122 controls aswitch 150. Theswitch 150 is connected between acurrent source 152 connected to ground and abridge circuit 154. Thebridge circuit 154 is formed by cross-coupled n-channel and p-channel enhancement metal-oxide-semiconductor field-effect transistor (MOSFET) pairs 156 and 158. Thefirst pair 156 has the source of a p-channel enhancement MOSFET 160 connected to VDD and the gates of the p-channel enhancement MOSFET 160 and anre-channel enhancement MOSFET 162 connected. The source of the n-channel enhancement MOSFET 162 is connected to theswitch 150. The second pair has the source of a p-channel enhancement MOSFET 164 connected to VDD and the gates of the p-channel enhancement MOSFET 164 and an n-channel enhancement MOSFET 166 connected. The source of the n-channel enhancement MOSFET 166 is connected to theswitch 150. The drains of the p-channel enhancement MOSFET 160 and the n-channel enhancement MOSFET 166 are connected and provide a TXP or transmit positive signal. The drains of the p-channel enhancement MOSFET 164 and the n-channel enhancement MOSFET 162 are connected and provide a TXM or transmit minus signal. The TXP and TXM signals are provided to the transmitterinductive loop 124 and aparallel capacitor 168. Theparallel capacitor 168 can be a separate capacitor or can be the inherent capacitance of the transmitterinductive loop 124. Achannel 170 is the isolation between the transmitterinductive loop 124 and the receiverinductive loop 126. In this configuration theMOSFETs inductive loop 124 and thecapacitor 168. - The RXP or receive positive and RXM or receive minus signals are developed across the receiver
inductive loop 126 and aparallel capacitor 172. Theparallel capacitor 172 can be a separate capacitor or can be the inherent capacitance of the transmitterinductive loop 126. The RXP signal is provided to the gate of an n-channel enhancement MOSFET 174, while the RXM signal is provided to the gate of an n-channel enhancement MOSFET 176. The drains of the n-channel enhancement MOSFET 174 and the n-channel enhancement MOSFET 176 are connected to VDD. The sources of the n-channel enhancement MOSFET 174 and the n-channel enhancement MOSFET 176 are connected to acurrent source 178, which is connected to ground. Acapacitor 180 is provided in parallel with thecurrent source 178. In this configuration theMOSFETs channel enhancement MOSFET 174 and the n-channel enhancement MOSFET 176 is also provided to the non-inverting input of acomparator 182, with the inverting input connected to VREF. The output of thecomparator 182 is the output of thedigital isolator 112. - In operation, when the input is a one or high, the
switch 150 is closed and thebridge circuit 154 is driving the transmitterinductive loop 124 to create the magnetic field captured by the receiverinductive loop 126. The signal from the receiverinductive loop 126 is rectified and compared to a reference. As theswitch 150 is closed, the rectified voltage will exceed the reference and thecomparator 182 will drive a high or one output. When the input signal is low, theswitch 150 is open and there is no magnetic field produced by the transmittinginductive loop 124, so the rectified voltage will be low, below the reference, and the output of thecomparator 182 is low or zero. - It is understood that these are example receiver and driver circuits for purpose of illustration and other designs can be used.
-
FIG. 2 illustrates an arrangement of loops and inductive loops according to the prior art. Afirst channel 202 has data flowing in one direction, while asecond channel 204 has data flowing in an opposite direction. The data in thefirst channel 202 is provided to a TX1 transmitterinductive loop 206, which is coupled to an RX1 receiverinductive loop 208. Similarly a TX2 transmitterinductive loop 210 receives the data being transmitted onchannel 2 and couples to an RX2 receiverinductive loop 212 to provide the data. In the drawing ofFIG. 2 , the fourinductive loops inductive loops channel inductive loops inductive loop inductive loops inductive loop FIG. 2 , which is not drawn to scale for illustrative purposes. These dimensions and numbers of turns are design-based and can vary as needed for a particular design.FIG. 2 shows exemplarymagnetic flux lines 220 emanating from TX2 transmitterinductive loop 210. As can be seen, the magnetic flux density in the RX2 receiverinductive loop 212 is not dissimilar to the magnetic flux density in the RX1 receiverinductive loop 208. This leads to a situation where the TX2 to RX1 crosstalk may actually exceed the TX1 to RX1 signal itself. Referring toFIG. 7 , the desired signal level is 320 mV while the crosstalk is 515 mV, actually higher than the signal level. This would result in significant data transmission errors. -
FIG. 3 is an alternate view of the inductive loops ofFIG. 2 . The view ofFIG. 3 is a side view, which shows that the third dimension of themagnetic flux lines 220 and the substantially coplanar nature of the adjacent channels. -
FIG. 4 shows a transmitterinductive loop 402 similar to the transmitterinductive loops inductive loop 404. The receiverinductive loop 404 has been reconfigured to be in roughly aFIG. 8 shape. Referring toFIG. 7 , this configuration of the receiverinductive loop 404 does reduce the crosstalk to a value of 30 mV but at the disadvantage of changing the impedance of the inductive loops. An inductive loop such as those of receiverinductive loop 208 and receiverinductive loop 212 have a tank impedance of 1.1 kΩ, while the configuration ofFIG. 4 has a tank impedance of 450Ω. This reduced impedance results in a reduced Q for the loop. Reducing the Q of the loop has the undesirable effect of impacting the signal-noise ratio (SNR) of the circuits, which complicates the entire design. - A alternative design is illustrated in
FIG. 5 , where the inductive loops ofFIG. 2 , referred to inFIG. 5 as a transmitterinductive loop 502 and a receiverinductive loop 504, are encircled by shielding 506 and 508. The shielding does reduce the crosstalk as indicated inFIG. 7 , where the crosstalk is reduced to the 160 mV but the presence of the shielding also further decreases the tank impedance to 620Ω as shown inFIG. 6 , again causing the impedance problems. The Q of the loop can be maintained but only at the expense further separating the various loops as greater distance is needed between the shields and the loops, which increase chip size undesirably. - Therefore, while the prior art does provide ways of reducing crosstalk, the prior art designs reduce the crosstalk at the expense of also decreasing the circuit impedance with its resulting problems of degraded SNR.
-
FIG. 8 is a drawing of a reduced crosstalk configuration which still maintains high impedance and high Q for the loops. The transmitterinductive loop 802 is configured similarly to that of theFIG. 2 prior art, such as transmitterinductive loops first portion 806 is a conventional portion, while asecond portion 808 is added which interacts with the flux lines inside the transmitterinductive loop 802. This means that the receiver inductive loop 804 is coupling with both positive and negative flux lines and their values are being summed. By properly sizing the areas of thefirst portion 806 and thesecond portion 808 and taking into account the densities of the flux lines, any crosstalk based on a signal from the transmitterinductive loop 802 is greatly reduced. - The crosstalk on the RX receiver inductive loop 804 based on the TX transmitter
inductive loop 802 is given by the following equation, where X is the RX receiver inductive loop 804 and Y is the TX transmitter inductive loop 802: - Where B is the magnetic flux density, d is the distance and A is the area.
- Because the RX receiver inductive loop 804 has a
first portion 806, X2, and asecond portion 808, X1, the equation is modified to account for the separate areas and the inversion of the magnetic flux between the twoportions - To make the crosstalk voltage zero, VX=0, assume that such is the case and then note that B+Y and B−Y are out of phase, which results in the following equation:
- This equation reduces to:
-
- In one design the ratio of B+Y:B−Y was 95:5, as the magnetic flux inside the loop is much greater than the magnetic flux outside the loop. Hence, the area of X2,
first portion 806, needs to be 95 times the size of the area of X1,second portion 808. This ratio will vary based on many factors, including loop size, loop spacing, number of turns and the like. - A ratio this size also means that the Q of the receiver inductive loop 804 is very close to the Q of the receiver
inductive loop 208, so that the impedance and other loop properties are effectively unchanged from the original receiverinductive loop 208. -
FIG. 11 illustrates the crosstalk change between the receiverinductive loop 208 and the receiver inductive loop 804. The 515 mV level of the noise without crosstalk cancellation according toFIG. 2 is illustrated in comparison to the 320 mV normal signal for the channel and the greatly reduced 20 mV signal for the crosstalk for the design ofFIG. 8 , where the receiver inductive loop has the two portions.FIG. 10 illustrates that the impedance of the receiver inductive loop ofFIG. 8 with the two portions is only nominally less than the receiver inductive loop of the prior art design ofFIG. 2 , which allows simplified circuit design. -
FIG. 9 illustrates the design ofFIG. 8 for two channels in different directions. A first channel TX1 transmitterinductive loop 902 is associated with a first channel RX1 receiverinductive loop 904. A second channel TX2 transmitterinductive loop 906 is associated with a second channel RX2 receiverinductive loop 908. The distances between the various transmitterinductive loops inductive loops FIG. 9 , the receiverinductive loop 908 for the second channel is receiving the normal amount of flux lines but the receiverinductive loop 904 of the first channel has minimal signal crosstalk because of the action of thesecond portion 905 located inside the transmitterinductive loop 906 of the second channel. - The inductive loops of the third and fourth channels are not illustrated by the receiver inductive loops do not contain the second portion located in the transmitter inductive loop of a different channel as the receiver inductive loop of the third channel is adjacent the receiver inductive loop of the second channel and not the transmitter inductive loop, as the channels are flowing data in the same direction. Similarly, the receiver inductive loop of the third channel is adjacent the receiver inductive loop of the fourth channel and not the transmitter inductive loop, as the channels are flowing data in the same direction. The receiver inductive loops with the portions inside the transmitter inductive loops are only needed for adjacent channels where data is flowing in different directions.
- By using the small receiver loop portion inside the transmitter inductive loop, the crosstalk is reduced so that a more manufacturable coplanar configuration can be used but the inductive loops can still be more compactly arranged.
- The above description is intended to be illustrative, and not restrictive. For example, the above-described examples may be used in combination with each other. Many other examples will be apparent upon reviewing the above description. The scope should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. In the appended claims, the terms “including” and “in which” are used as the plain-English equivalents of the respective terms “comprising” and “wherein.”
Claims (19)
Priority Applications (3)
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US16/021,175 US10855333B2 (en) | 2018-06-28 | 2018-06-28 | Crosstalk reduction in receiver inductive loop using capturing loop in transmitting inductive loop |
PCT/US2019/038651 WO2020005797A1 (en) | 2018-06-28 | 2019-06-24 | Crosstalk reduction in receiver inductive loop |
US17/076,275 US20210036735A1 (en) | 2018-06-28 | 2020-10-21 | Crosstalk reduction in receiver inductive loop using capturing loop in transmitting inductive loop |
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US16/021,175 US10855333B2 (en) | 2018-06-28 | 2018-06-28 | Crosstalk reduction in receiver inductive loop using capturing loop in transmitting inductive loop |
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US17/076,275 Continuation US20210036735A1 (en) | 2018-06-28 | 2020-10-21 | Crosstalk reduction in receiver inductive loop using capturing loop in transmitting inductive loop |
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US17/076,275 Abandoned US20210036735A1 (en) | 2018-06-28 | 2020-10-21 | Crosstalk reduction in receiver inductive loop using capturing loop in transmitting inductive loop |
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WO2022000207A1 (en) * | 2020-06-29 | 2022-01-06 | 深圳市速腾聚创科技有限公司 | Laser receiving device and laser radar |
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US11792051B2 (en) | 2020-07-17 | 2023-10-17 | Texas Instruments Incorporated | Multi-channel digital isolator with integrated configurable pulse width modulation interlock protection |
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JPH0371406A (en) * | 1989-08-11 | 1991-03-27 | Pioneer Electron Corp | Magnetic head and its production |
US5004317A (en) * | 1990-01-03 | 1991-04-02 | International Business Machines Corp. | Wire bond connection system with cancellation of mutual coupling |
JPH07271928A (en) * | 1994-03-29 | 1995-10-20 | Hitachi Ltd | Non-contact parallel data transfer device and memory card |
US6442213B1 (en) | 1997-04-22 | 2002-08-27 | Silicon Laboratories Inc. | Digital isolation system with hybrid circuit in ADC calibration loop |
US6891731B1 (en) * | 1999-11-01 | 2005-05-10 | Advanced Micro Devices, Inc. | Crosstalk cancellation for integrated circuit package configuration |
US8049573B2 (en) | 2004-06-03 | 2011-11-01 | Silicon Laboratories Inc. | Bidirectional multiplexed RF isolator |
WO2009130665A1 (en) * | 2008-04-21 | 2009-10-29 | Nxp B.V. | Planar inductive unit and an electronic device comprising a planar inductive unit |
RU97875U1 (en) | 2010-02-24 | 2010-09-20 | ЗАО "РАДИУС Автоматика" | MULTI-FUNCTION RELAY PROTECTION DEVICE FOR SUBSTATIONS AND DISTRIBUTED ITEMS WITHOUT BATTERY BATTERIES |
CN107078977B (en) * | 2014-09-24 | 2020-10-16 | 美国亚德诺半导体公司 | Circuit and system for multipath isolator communication |
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2018
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WO2022000207A1 (en) * | 2020-06-29 | 2022-01-06 | 深圳市速腾聚创科技有限公司 | Laser receiving device and laser radar |
CN114207464A (en) * | 2020-06-29 | 2022-03-18 | 深圳市速腾聚创科技有限公司 | Laser receiving device and laser radar |
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